In the normal heart, the ventricles pump at the about the same time in a manner synchronized with the atria. When a patient has heart failure, often times the right and left ventricles do not pump together, which is referred to as dysynchrony. If dysynchrony is significant, the heart has less time to fill with blood and cardiac output drops.
Biventricular pacing therapy and, in particular, cardiac resynchronization therapy (CRT), aims to synchronize the right and left ventricles via delivery of appropriately timed stimulation to each ventricle. With respect to such timed stimulation, various parameters are involved, including atrio-ventricular delay and interventricular delay. Clinical studies related to biventricular cardiac pacing therapy have shown that use of an optimal atrio-ventricular delay (e.g., AV delay) and an optimal interventricular delay (e.g., VV delay) can improve cardiac performance. However, such optimal delays depend on a variety of factors.
Optimization of AV delay or VV delay may occur at implantation and sometimes, a re-optimization may occur during a follow-up consultation. Recently, techniques have been disclosed for optimization algorithms that may periodically re-optimize without any intervention. Regardless of where, who or what performs an optimization or re-optimization, the health of the CRT patient should be a concern as timings should not be adjusted without a substantial purpose for doing so.
Conventional implantable devices typically include algorithms that respond to a condition by adjusting one or more timings. For example, as fusion beats are sometimes detected as loss of capture, a single detection of loss of capture does not necessarily mean that the stimulation amplitude is too small and that a capture threshold search needs to be conducted; instead, a fusion beat could also have occurred. Thus, conventional implantable devices typically implement an automatic fusion avoidance response after the first loss of capture to rule out the possibility of initiating a threshold search on a fusion beat. In general, such conventional fusion avoidance algorithms increase the AV or PV delays in dual-chamber devices and reset the basic interval on the backup pulse in single chamber devices. As already mentioned, for heart failure patients undergoing CRT, AV and VV delays are of very high importance and should be adjusted only if needed or circumstances permit doing so without substantial detriment to the patient. Thus, a need exists for fusion detection or other techniques to distinguish true loss of capture from fusion without a need to change timings. Various exemplary technologies presented herein address this need and other needs.